The invention is particularly useful, in combination with a plumb bob, in inspecting, constructing and installing parts for accuracy. It is especially useful in checking the installation of metal door frames such as steel door frames, for true. Door frames must be installed to a high accuracy if the associated door is to be properly installed. The legs of the door frames should be vertical, that is, they should be at right angles to the horizontal plane, (the X axis and the Y axes). The vertical orientation of the door should be true to both the X and Y axes.